There are many applications where it is desirable and necessary to trace or locate the position of a concealed element, such as an underground cable or pipe. In cases where such a concealed element is electrically conductive, techniques have been proposed in the past for coupling an electrical signal to the element, typically at a high enough frequency so as to produce above-ground radiation. A portable receiver, tuned to the particular frequency, is then walked over the ground, and conventional triangulation techniques used to pinpoint the location and path of the element.
A problem which has been encountered in the past is that there may easily be a wide mismatch between the output impedance of the signal generator, or transmitter, employed and the impedance of the buried pipe, or cable, into which the signal is coupled. This can result in a very weak radiation signal which is difficult to monitor. To rectify this situation, proposals have been made for manually adjustable impedance-matching circuitry in a transmitter, which circuitry is adjustable by an operator to produce as close as possible an impedance match between a transmitter and a coupled pipe or cable.
However, very often operators simply do not pay adequate attention to impedance-matching procedures, and are often found to forget easily exactly what this procedure is. Further, even where, in such equipment, impedance matching has been properly performed at the beginning of a search operation, it is not uncommon to have a weather condition, or some other condition, change during the operation which radically modifies the impedance of the buried element. For example, if one starts a search operation in perfectly dry weather, one impedance match will suffice; but if, during a search operation, there should be a rainstorm which sufficiently wets the ground, a considerably different impedance match will then be required. If this occurs when the operator is some distance away from the transmitter, it will be necessary for him to return to the site of the transmitter, in order to make an appropriate adjustment, before he can continue an adequate search.
A general object of the present invention, therefore, is to provide unique means, in apparatus of the type generally described above, for greatly simplifying the problem of obtaining an impedance match of the kind indicated.
More specifically, an object of the invention is to provide such means which functions to produce automatic impedance-matching within a preselected range of potential impedances, thus eliminating a major source of operator error.
Still another object of the invention is to provide such means which accomplishes the stated function through monitoring the level of output current from a transmitter in the apparatus, and which automatically seeks to maximize this current.
Various other objects and advantages that are attained by the invention will become more fully apparent as the description which now follows is read in conjunction with the accompanying drawings.